Add option to configure the hashing algorithm used

[ericcornelissen]

Summary

Currently ghasum supports only one hashing algorithm. This should be configurable by users so that alternatives can be used and migration to newer algorithms can be done gradually.

Proposal

• The hashing algorithm to be used must be a CLI option on the ghasum init command.
• The hashing algorithm must be upgradable for a project that already uses ghasum, e.g. with a command like ghasum upgrade¹ or with a CLI flag on ghasum update.
• The hashing algorithm used must be recorded in the gha.sum file so that the ghasum CLI knows which algorithm it should use for that project when verifying or updating.

Footnotes

1. Note that the command ghasum upgrade is probably too generic and may want to be used for other purposes in the future (e.g. upgrade from one sumfile version to the next). ↩